The present invention relates to electric circuit contactor systems and, more particularly, to an electromagnetically actuated pneumatic control valve for an electrical circuit contactor.
Traction vehicles such as locomotives, off-highway earth-moving vehicles and transit cars, are commonly powered by electric motors coupled in driving relationship to wheels and/or axles of the vehicles. Control of the electric motors requires an onboard electric power control system for supplying controlled electric power to the motors in response to an operator demand for horsepower or speed. Since the electric motors are typically high horsepower motors having operating current of as much as 1000 amperes and peak operating voltages of as much as 1000 volts, the control systems commonly use high voltage, high current contactors in several applications. Because it is desirable to open and close such contactors rapidly to minimize arcing and further because of the mass of the moveable contact portion of such contactors, it is common to utilize pneumatic cylinders or actuators for actuating such contactors. The pneumatic actuators require the use of control valves for controlling the application of air to the actuators.
One form of control valve used in traction vehicles is the "magnet valve". This valve is essentially an electromagnetic solenoid coupled to a pneumatic valve. The pneumatic valve is generally a three-port device having an air inlet port, an air outlet port for connection to an actuator and an air exhaust port for deeding air from the actuator. The valve may control air at a nominal 80 psia.
Pneumatic valves used in magnet valves have been taken from similar valves used in stationary installations. The application of these valves in traction vehicles places the valves in a relatively hostile environment, i.e., the air which is passed through the valve is generally contaminated with dirt or other debris. Further, the availability of an adequate air supply is limited and valves which are designed to "leak" must now provide better sealing so as to minimize air loss. With better seals, debris which was previously tolerated must be eliminated to protect the sealing surfaces.